International treaties: their character; their forms; their different species.—Essential conditions for public treaties: they are the same as for private contracts.
Observance of treaties.—Obligatory character of treaties: testimony of Cardinal Richelieu.
The human race being divided into divers particular societies called States or nations, those different bodies stand toward each other as individuals; they are subject to the primitive laws existing naturally among all men, and they are obliged to practice certain duties toward each other.
112. International law.—General principles.—It is this body of laws which is called international law, and which is nothing more than the natural law itself, or the moral law applied to nations.
It is by virtue of this natural law that the nations ought to consider each other equals, and independent of each other; that they should not injure each other, and should make each other, on the contrary, reparation for injury done. Hence the right of self-defense in case of attack, of repelling and restraining by force whatever violence may threaten or oppress them.
When nations practice toward each other the prescriptions of the natural law, they are in a state of peace with each other; when they are obliged to resort to force to repel injustice, they are in a state of war.
113. War.—It is evident that in all nations the ruler, whoever he be (the people, nobles, or king), ought to have the right to carry on war; for it is nothing else than the right of self-defense, and this right is the same for the nation as for individuals. War is, then, legitimate in principle; but in fact, it may be just or unjust according as it takes place for good or bad reasons, and sometimes for no reason at all.
114. Reasons of a just war.—It is not easy to say in advance and in a general manner, what may be the reasons of a just war; for they vary according to circumstances; they may be all reduced to one fundamental principle, namely, the defense of the national territory when threatened. Moreover, a war may be undertaken not only in self-defense, but to protect allies when they are unjustly attacked. As for the following reasons, more or less frequently alleged as pretexts for war, good morality cannot justify them:
1. Thus, the fear of the powerful neighbor, giving, for example, as a pretext that he erects new citadels on his lands, organizes an army, increases his troops, etc., is not a sufficiently just reason for war.
2. Utility does not give the same right as necessity: for example, arms could not legitimately be resorted to in order to gain possession of a place which might suit our convenience, and be proper to protect our frontiers.